1. Field of the Invention
The present invention relates to microelectronic spring contacts such as are used in semiconductor wafer testing and other electronic connection applications. More particularly, the invention relates to a method for repairing individual spring contacts without causing appreciable damage to adjoining spring contacts of an array.
2. Description of Related Art
Microelectronic spring contacts, such as disclosed, for example, by U.S. Pat. No. 5,476,211, are known in the art and have been applied in fine-pitch, high-density arrays for various applications. For example, microelectronic spring contacts of various types have been used on probe cards for contacting semiconductor wafers during testing, on interposers used in probe card assemblies, directly on semiconductor wafers and chips, and in connectors for mounting semiconductor components to test or production substrates. Such applications typically demand that a large plurality of almost microscopic spring contacts be arrayed in a high-density, fine-pitch array over an electronic substrate. For example, it is not unusual for hundreds or even thousands of microelectronic spring contacts to be arrayed over an area of a few square centimeters.
The individual spring contacts, however, may be damaged during manufacture or post-manufacturing handling or use. The damage may reduce the performance of the spring contacts or even render them unusable. Prior efforts to repair fine-pitch, high-density arrays of microelectronic spring contacts have been limited to reshaping (bending) individual spring contacts that are bent out of shape. When spring contacts were defective or damaged in such a way that they could not be repaired by reshaping, there was no way to repair or replace the defective spring contacts and thus save the entire array.
Prior limitations in the repair of individual spring contacts stem from the methods for making high-density spring contact arrays. Such arrays are not made by assembling individually formed spring contacts on a substrate. Instead, the entire array is formed en masse with each microelectronic spring contact formed in position on a substrate. For example, some methods of making microelectronic spring contacts, such as disclosed in U.S. Pat. Nos. 5,476,211, 5,919,707, and 6,110,823, all of which are incorporated by reference herein in their entirety, involve bonding relatively soft gold wires to a substrate while shaping the wires to the desired spring contact shape. The shaped wires are then electroplated together to build up a structural layer that stiffens the spring contacts and imparts the required strength and resiliency. Similarly, other methods, such as disclosed in U.S. Pat. No. 6,255,126 and in commonly-owned U.S. application Ser. No. 09/023,859, filed Feb. 13, 1998; Ser. No. 09/474,788, filed Dec. 29, 1999; and Ser. No. 09/364,855, filed Jul. 30, 1999, all of which are incorporated by reference herein in their entirety, involve building arrays of spring contacts on substrates using lithographic and electroplating techniques to form individual spring contact elements together in an array. Methods such as these are generally not suitable for replacing an individual spring contact in a completed array, because surrounding spring contacts of the array would impair and/or be damaged by the plating, etching and/or other operations needed to repair or replace the damaged spring contact.
It is desired, therefore, to provide a method for repairing or replacing an individual damaged spring contact of a fine-pitch, high-density array of microelectronic spring contacts.
The present invention provides a method for repairing an individual spring contact of a microelectronic spring contact array without adversely affecting other spring contacts of the array. The method may be easily and quickly implemented using processing equipment and tools such as are used for the manufacture of the microelectronic spring contact arrays themselves. Using the method, high density arrays such as used, for example, on probe cards for wafer testing applications, may be repaired at a much lower cost, and much more quickly, than replacing the entire array with a new array.
According to an embodiment of the invention, a damaged spring contact is removed from the substrate of a contact array and replaced by a specially shaped replacement spring contact. The damaged spring contact may be removed by cutting through the spring at a location adjacent to the substrate. Less preferably, the damaged spring contact may be removed by heating the base of the spring contact using a localized method, such as an electrode or laser. In the case of cutting the spring, the damaged spring may, and generally does, leave behind a stub attached to a terminal of the substrate. The uneven surface presented by the stub and terminal should be accounted for in the design of a replacement spring. It is generally not practical to planarize a single terminal for a replacement spring without damaging or contaminating the surrounding array.
A replacement spring contact for the removed spring contact may be formed by any suitable method. Preferably, the replacement spring contact is formed by defining the spring contact profile in a recess of a sacrificial layer over a sacrificial material, and plating up a spring contact material in the recess. A relatively complex replacement spring contact may thus be formed at a very small scale (e.g., microscopic or nearly microscopic) in a single plating cycle. Preferably, a plurality of similar replacement spring contacts are formed together and optionally attached together by tie bars not unlike a connecting sprue of co-molded injection molded parts. Individual replacement spring contacts may then be conveniently stored together and removed from the tie bars as needed. This profile-defining lithographic method is believed best for forming relatively small quantities of free-floating, relatively complex spring contact shapes, and hence is preferred for forming replacement spring contacts.
Nevertheless, alternative methods for forming the replacement spring contact may include stamping, punching, or cutting, such as by using a laser; or metal molding techniques such as powder metal metallurgy. These methods may be less suitable for forming replacement spring contacts at very small scales. Other alternative methods include the wire forming/plating and lithographic techniques such as disclosed in the references cited above, or some combination thereof. Such methods may be adapted to form replacement spring contacts on a sacrificial substrate, and then the sacrificial substrate may be removed to provide a free-floating spring. These wire-forming and lithographic methods are effective at very small scales, but may require more production steps to produce a replacement spring contact than the preferred method described above.
However the replacement spring contact is formed, the final spring contact may need to conform to exacting specifications for the removed spring contact. In general, the replacement spring contact should be shaped to present a contact tip in the same location as the removed spring contact. Furthermore, the replacement spring contact should have spring characteristics, including spring constant, yield strength, and fatigue strength, that are the same or similar to the removed spring contact""s design values. The replacement spring contact should deflect in both z and x directions (i.e., perpendicular and parallel to the support substrate) within the tolerances for the design values of the removed spring contact. For example, the replacement spring contact should exhibit a wiping action (x deflection) within the design tolerance for the removed spring contact. The replacement spring contact should have electrical characteristics that meet the requirements of the spring contact array, and should be bonded to the terminal of the removed spring contact in a way that does not interfere with adjoining spring contacts or terminals.
In an embodiment of the invention, the replacement spring contact has a shape that is similar to the removed spring contact, except for at its base. The base of the replacement spring contact is preferably shaped to fit over the terminal from which the damaged spring has been removed, including any protruding posts or stubs that may remain on the terminal after the damaged spring contact has been removed. In an embodiment of the invention, the replacement spring contact differs from the removed spring contact in having a base formed of two or more spaced-apart legs connected by a base. The legs and connecting base may be designed to span the terminal of the removed spring contact, or a portion thereof. A resilient, cantilevered arm, having a shape that may be similar to the cantilevered portion of the removed spring contact, extends from the base in a direction opposite to the legs. The spaced apart legs are designed to accommodate any unevenness in the terminal of the removed spring, such as may be created by the stub of the removed spring contact. In alternative embodiments, the base of the replacement spring may be flat, or may include one or more recesses to fit over protrusions on the terminal.
To replace the removed spring, a bonding material, such as a solder paste, is applied to the terminal of the removed spring. The replacement spring is then positioned on the solder paste (or other bonding material) with its legs positioned around or near the periphery of the terminal, and aligned so that its contact tip is as close as possible to the design tip position for the removed spring. The replacement spring is then soldered or bonded in place, such as by connecting an electrode to the base of the spring and passing a current through the electrodes, thereby generating localized heat. After the solder hardens, minor corrections may be made to the contact tip position by manual adjustment (bending) of the spring""s cantilever arm.
It should be appreciated that the foregoing method for replacing a damaged spring contact may, of course, also be used to form spring contacts in an original component. In such case, the step of removing the damaged spring contact is omitted, and the remaining steps may be performed as previously described above.
A more complete understanding of the method for repairing a microelectronic spring contact will be afforded to those skilled in the art, as well as a realization of additional advantages and objects thereof, by a consideration of the following detailed description of the preferred embodiment. Reference will be made to the appended sheets of drawings which will first be described briefly.